Add code components 366-385; ScrollArea Follow, editor sync

A terminal with history, a Go-colored code block, a log viewer that
follows, a hex viewer, a memory map, a JSON tree, a line diff, a GAME
OVER crash screen, an FPS meter, profiler bars, breakpoints,
variables, command history, a shortcut list, a debug grid, a pixel
editor that exports string art, a palette editor, a sprite sheet, a
glyph map and a 6502 register view.

layout.ScrollArea takes Follow, and ChatLog now uses it. data.TreeNode
takes a Value drawn in its Slot. pixel gains Has, and Sprite.Art
writes MustSprite art. pixel.Editor takes the caller's value at each
input event, so a value changed between frames is never typed onto.

code/registerview.go

@@ -0,0 +1,104 @@
+package code
+
+import (
+	"fmt"
+	"strings"
+
+	"github.com/egoist/mygo/ui"
+
+	"git.zacharyzhang.com/ZacharyZhang-NY/8bitMyGoUI/pixel"
+)
+
+// CPU is a 6502's registers; P holds the flags.
+type CPU struct {
+	A, X, Y, SP, P uint8
+	PC             uint16
+}
+
+type RegisterViewOptions struct{}
+
+type regKey struct{}
+
+// seen is the CPU last shown and bits it flipped.
+type seen struct {
+	cpu, flipped CPU
+}
+
+const flags = "NV-BDIZC"
+
+// RegisterView shows registers and flags; the last change lights.
+func RegisterView(c *ui.Context, text string, cpu CPU, o RegisterViewOptions) *ui.Element {
+	k := pixel.K(c)
+	col := ui.Column(c).Gap(k.D(1)).Role(ui.RoleGroup).Label(text)
+	sn := ui.Local(col, regKey{}, func() seen { return seen{cpu: cpu} })
+	if cpu != sn.cpu {
+		was := sn.cpu
+		sn.cpu, sn.flipped = cpu, CPU{A: was.A ^ cpu.A, X: was.X ^ cpu.X, Y: was.Y ^ cpu.Y, SP: was.SP ^ cpu.SP, P: was.P ^ cpu.P, PC: was.PC ^ cpu.PC}
+	}
+	fl := sn.flipped
+	return col.Children(func() {
+		for _, r := range []struct {
+			name      string
+			v, change uint16
+			wide      bool
+		}{
+			{"A", uint16(cpu.A), uint16(fl.A), false}, {"X", uint16(cpu.X), uint16(fl.X), false}, {"Y", uint16(cpu.Y), uint16(fl.Y), false},
+			{"SP", uint16(cpu.SP), uint16(fl.SP), false}, {"PC", cpu.PC, fl.PC, true},
+		} {
+			digits := 2
+			if r.wide {
+				digits = 4
+			}
+			hexed := fmt.Sprintf("$%0*X", digits, r.v)
+			ui.Box(c).Size(k.D(120), k.D(pixel.LineHeight)).Role(ui.RoleText).Label(r.name + " " + hexed).Draw(func(p *ui.Painter, rc ui.Rect) {
+				g := k.Canvas(p, rc)
+				g.Micro(0, 4, r.name, pixel.Faint, 1)
+				ink := pixel.Ink
+				if r.change != 0 {
+					ink = pixel.Accent
+				}
+				g.Text(12, 0, hexed, ink, 1)
+				if !r.wide {
+					bits(g, 52, uint8(r.v), uint8(r.change))
+				}
+			})
+		}
+		set := []string{}
+		for i := range 8 {
+			if cpu.P&(0x80>>i) != 0 && flags[i] != '-' {
+				set = append(set, string(flags[i]))
+			}
+		}
+		ui.Box(c).Size(k.D(8*9), k.D(14)).Role(ui.RoleText).Label(fmt.Sprintf("P $%02X", cpu.P)).Description(strings.Join(set, " ")).Draw(func(p *ui.Painter, rc ui.Rect) {
+			g := k.Canvas(p, rc)
+			for i := range 8 {
+				x, on, flip := i*9, cpu.P&(0x80>>i) != 0, fl.P&(0x80>>i) != 0
+				fill, ink := pixel.Well, pixel.Faint
+				if on {
+					fill, ink = pixel.Good, pixel.AccentInk
+				}
+				edge := pixel.Shade
+				if flip {
+					edge = pixel.Accent
+				}
+				g.Rect(x, 0, 8, 14, edge)
+				g.Rect(x+1, 1, 6, 12, fill)
+				g.Micro(x+3-1, 5, string(flags[i]), ink, 1)
+			}
+		})
+	})
+}
+
+// bits draws v's eight bits; flipped ones light.
+func bits(g pixel.Canvas, x int, v, flipped uint8) {
+	for i := range 8 {
+		b, ink := "0", pixel.Faint
+		if v&(0x80>>i) != 0 {
+			b, ink = "1", pixel.Ink
+		}
+		if flipped&(0x80>>i) != 0 {
+			ink = pixel.Accent
+		}
+		g.Micro(x+i*4+i/4*2, 4, b, ink, 1)
+	}
+}